1. Field of the Invention
The present invention relates to a viscous fluid transfer apparatus and method for transferring a viscous fluid to the connecting terminal of a package component such as an IC. The present invention also relates to an electronic component mounting apparatus and method using the viscous fluid transfer apparatus, and a semiconductor device. Moreover, the present invention particularly relates to a three-dimensional mounting technique for providing an electronic component in plural stages.
2. Description of the Related Art
In the recent electronic apparatus industry, a high functionality and a reduction in a size and a weight of a product have been vigorously developed, and various mounting methods such as double-sided mounting have been employed for an electronic component such as an IC in order to reduce a mounting area to a circuit board in addition to an increase in the integration of a semiconductor device itself.
In the package technique of the electronic component, moreover, a DIP (Dual Inline Package) which has conventionally been used widely is switched to a QFP (Quad Flat Package) and an SOP (Small Outline Package) which have a space between leads as shown in a double-sided mounting state of FIG. 58(a), and furthermore, attention has been paid to an area array type package such as a BGA (Ball Grid Array) or a CSP (Chip Size Package) shown in FIG. 58(b) as a technique for a practical stage.
On the other hand, a bare chip mounting method for carrying out direct mounting onto a circuit board without packaging has also been partially employed. However, there has still been a problem to be solved for a mass production and a reduction in a cost. In the bare chip mounting method, a flux is transferred onto a bare chip component to be mounted on a circuit board. In this case, examples of a flux transfer device for transferring the flux include a device for forming the transfer surface of the flux by reciprocating a squeegee 512 having almost the same structure over a transfer unit 510 as shown in FIGS. 59(a), 59(b), 60(a), and 60(b). The bare chip component is mounted by moving the squeegee 512 over the transfer unit 510 to extend the flux over the whole pan surface and immersing the bare chip component on the extended flux to transfer the flux to the component side, and by pressure welding the bare chip component into a predetermined position on the circuit board after the transfer.
Moreover, there have been various methods for mounting the electronic component of the area array type package onto the circuit board, and the mounting can be carried out in the following manner, for example. First of all, a land is formed in a position on the circuit board corresponding to the solder ball of an electronic component (BGA) and a solder cream is mask printed on the land. Then, the electronic component is mounted in the predetermined position on the circuit board to superpose the printed solder cream on the solder ball of the electronic component, and the electronic component is temporarily fixed to the circuit board with the viscosity of the solder cream. The circuit board is subjected to a reflow process so that the solder cream and the solder ball are molten and the land and the solder ball of the electronic component are connected and fixed to each other.
In the mounting method for the electronic component of the conventional area array type package, however, a reduction in a mounting area has further been required. And furthermore, a mask hole forming technique having high precision for a solder cream printing screen and a mask aligning technique have been required with an enhancement in the fine pitch of the electronic component. For this reason, stable mounting having high precision has been restricted over the extension of a current method and it is inevitably hard to carry out further high density mounting so that the development of other different mounting methods has been desired.
A technique for forming an electronic component with a stack structure having several stages has variously been investigated. However, the electronic component is not simply stacked but a jig accommodating the electronic component therein is provided or a contact structure is very complicated. Consequently, there has been a problem in that the design of a conventional circuit pattern is forcibly changed considerably and a mounting cost is hard to reduce.
Moreover, it has also been supposed that the electronic component is three-dimensionally mounted by stack on a rear face opposite to the mounting surface side of the electronic component for an area array type package such as a BGA or a CSP having the small pitch of a connecting terminal. There has been a problem in that a method of giving a solder cream for the stack is to be established or alignment precision is to be maintained. Therefore, the practical use has not been attained.
When a solder cream is to be put and transferred onto the electronic component in place of the flux by using the flux transfer device for transferring the flux onto the bare chip component, the viscosity of the solder cream is extremely higher than that of the flux. Therefore, the solder cream overflows from the transfer unit so that the flux transfer device cannot be actually substituted for solder cream transfer.
FIGS. 59(a), 59(b), 60(a) and 60(b) show a state in which the solder cream is put onto the flux transfer device to move the squeegee 512, (a) being a plan view and (b) being a side view. As shown in FIGS. 59(a) and (b), when the squeegee 512 is moved from the left side to the right side in the drawing, the solder cream is protruded from the end in the longitudinal direction of the squeegee 512 based on a difference in a viscosity so that it overflows from the edge portion of the transfer unit 510. In the same manner as in FIGS. 60(a) and (b), when the squeegee 512 is moved from the right side to the left side in the drawing, the solder cream further overflows.
In addition, the solder cream coming in contact as shown in FIG. 61 is transmitted toward the upper part of each squeegee 512 due to a viscosity thereof, and finally, the solder cream sticks to each portion of the apparatus and the solder cream is dropped off from a part of the apparatus. As a result, the solder cream is scattered to the surrounding environment so that maintenance is often required. Consequently, a manufacturing man-hour is increased and the quality of a product is deteriorated.
Moreover, there is also a problem regarding a sucking nozzle 514 to be used for the transfer of the solder cream. More specifically, as shown in FIG. 62, when an electronic component 520 is to be pushed against an inclined surface, for example, the solder cream is to be transferred to the electronic component 520 by using the transfer unit 510 having the inclined pan surface, the sucking nozzle 514 usually has a sucking tip portion 514a formed of a metal and the rear face of the electronic component 520 is inclined. Therefore, a clearance is generated between the sucking tip portion 514a and the rear face of the electronic component 520 so that air leaks from the clearance and suction cannot be carried out.
It can be proposed that a component sucking property can be improved by attaching a rubber pad 516 to the sucking tip portion 514a. However, when the solder cream is to be transferred to the electronic component 520 as shown in FIG. 62, for example, the rubber pad 516 is elastically deformed and contracted in the direction of push-in so that a push-in depth cannot be controlled even if the electronic component 520 is pushed in from the surface of the solder cream up to a predetermined depth. Thus, if the solder cream cannot be given to the electronic component necessarily and sufficiently, connection cannot be carried out reliably so that the conduction failures of the electronic component after mounting or mechanical fixing failures might be caused.
The invention has been made in consideration of the conventional circumstances. It is the first object of the invention to provide a viscous fluid transfer apparatus and a transfer method for transferring a viscous fluid to the terminal portion of an electronic component and laminating an electronic component, in order to increase a space efficiency to mount an area array type package component to a circuit board at a high density.
Moreover, it is the second object of the invention to provide an electronic component mounting apparatus and a mounting method of laminating and mounting an electronic component onto a circuit board by using the viscous fluid transfer apparatus and the transfer method.
Furthermore, it is the third object of the invention to provide a semiconductor device capable of carrying out high density mounting as a stack structure having plural stages.